1. Field of the Invention
The present invention generally relates to a semiconductor device, to a method for forming a semiconductor device, and to a data processing system.
Priority is claimed on Japanese Patent Application No. 2010-230746, filed Oct. 13, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
In recent years, large-scale integrated (referred to as LSI hereinafter) circuits, in which a large number of MOS transistors are integrated onto one semiconductor chip have been adopted in the main parts of computers and electrical equipment. Among LSI devices, elements such as DRAMs (dynamic random-access memories) have seen a rapid shrinking of element size, accompanied by progressively shorter MOS transistor gate lengths. By integrating a large number of MOS transistors in a memory cell region 101, the distance between adjacent MOS transistors has also become short, and the shorter the gate length becomes, the greater is a deterioration of transistor characteristics by the short channel effect of the MOS transistor.
Japanese Unexamined Patent Application, First Publication, No. JP-A-2008-300843 discloses that a MOS transistor (buried-gate MOS transistor) is formed to have a word line that functions as a gate electrode is buried into a groove formed within a semiconductor substrate in order to suppress this type of MOS transistor short-channel effect. The upper part of the word line on the inside of the groove is buried with an insulating film. Because in a buried-gate MOS transistor there is an impurity diffusion layer at the surface part of the active region between word lines, it is possible to establish physically an effective channel length (gate length) having a given length. For this reason, buried-gate MOS transistors have structures that can be applied to the reduction of the size of cell transistors in DRAMs.
Japanese Unexamined Patent Application, First Publication, No. JP-A-11-307626 discloses a method of filling the inside of a groove with a silicon oxide film using the spin-coating method, which is known as a method for burying the inside of a groove with an insulating film.